ABSTRACT

The genus Eutatus has been recently revised and only two species were recognized over detailed study of the characteristics of fixed osteoderms from the pelvic shield and other elements of postcranium: E. seguini, limited to the Bonaerian Stage/Age and Lujanian Stage/Age, and E. pascuali, older than the latter, recognized in the Marplatan and Ensenadan Stage/Age. Here, we report a new species of Eutatini, Eutatus crispianii sp. nov., occurring in the Lujanian Stage/Age and described on the basis of the morphology of fixed osteoderms. Geometric morphometric analysis and statistical analysis of quantitative variables of these elements reveal significant differences between the new species and those previously reported.

Final citation: Brambilla, Luciano and Ibarra, Damián Alberto. 2017. A new species of Eutatus Gervais (Xenarthra, Dasypodidae) from the Late Pleistocene of the Northern Pampean Region, Argentina. Palaeontologia Electronica 20.1.13A: 1-9. https://doi.org/10.26879/676 palaeo-electronica.org/content/2017/1767-a-new-species-of-eutatus

http://zoobank.org/06362661-78A8-424E-849B-1F11AC171F66

INTRODUCTION

Armadillos (Mammalia, Dasypodidae) belong to a particular group present in the faunas of Pampas from the late Miocene to Holocene (Vizcaíno and Bargo 1993; Vizcaíno et al., 1995, Soibelzon et al., 2010; Soibelzon and Leon, 2017). These organisms have, as one of their most notable features, an articulated bony carapace consisting of several hundred of interlocked osteoderms. Eutatus is a genus of extinct large armadillos that could have reached weights of around 50 kilograms (Scillato-Yané et al., 1995; Vizcaíno and Bargo, 2013). Two thirds of the anterior region of the body was covered with mobile osteoderms arranged in about 14 articulated bands. The scapular shield was practically missing as it was rudimentary and limited to the flanks of the carapace. The posterior third was covered by a pelvic shield consisting of fixed osteoderms (Krmpotic et al., 2009a).

The remains of Eutatus are abundant from Chapadmalalan to Lujanian Stage/Age (Krmpotic and Scillato-Yané, 2007) and although there are some partial or complete carapaces, most specimens are composed of a single or a few osteoderms.

Paul Gervais (1867) was the first to describe Eutatus and the species E. seguini and then Ameghino (1881, 1889) and Bordas (1932) added new species: E. brevis, E. minutus,E. punctatus and E. ameghinoi (Krmpotic et al., 2009a). However, further review indicated that there are no characters that may support the validity of all these species. For example, E. minutus was described based on a group of small osteoderms that in fact belong to the anterior bands of the carapace of E. seguini (Krmpotic et al., 2009a). Given these circumstances the species were synonymized by Scillado-Yané (1982), who recognized only the type species E. seguini. Recently Krmpotic et al. (2009a) described a new species: E. pascuali, restricted to Marplatan-Ensenadan whereas E. seguini has been circumscribed to the Bonaerian-Lujanian. Here we present a new species of armadillo of the Pampas belonging to the genus Eutatus; its remains were found in Santa Fe, in sediments corresponding to the Saladillo Formation (Pleistocene-Holocene) (Parent et al., 2010). We carry out a statistical analysis on quantitative characters of fixed osteoderms, and we applied a geometric morphometric analysis to study the shape of osteoderms. These results support the description of the new species and strengthen knowledge on the morphology of osteoderms of Eutatus.

MATERIAL AND METHODS

We follow the chronological and biostratigraphic schemes of Cione and Tonni (2005). The terminology for description of osteoderms follows Krmpotic et al. (2009a).

The description of the new species was based on the study of dorsal osteoderms from the pelvic shield. Consequently, we adopted the criterion of comparing homologous regions used in Krmpotic et al. (2009a). The osteoderms of the holotype of E. crispianii sp. nov. were measured and compared with those from individuals of previously described species of Eutatus. A random effects model was used to estimate mean, variance between specimens, and variance within specimens of variables length and width from fixed osteoderms. The equation used is described: yij = β + bi + eij; where yij is the i-th observation of the variable under study in the specimen j; β, the average value of the variable under study (width or length); bi, the random effect of the ith-specimen and eij the random error. These parameters were used to test if there are significant differences in the length and/or width of osteoderms between the species of Eutatus. For this purpose, a total of 201 osteoderms of museum collections from Argentina were evaluated. Only the well-preserved fixed osteoderms of the dorsal region of the pelvic shield were analyzed.

Statistical analyses were performed using SPSS v20 (IBM Corp, 2011). Specimens previously assigned to E. pascuali and E. seguini were also analysed together in order to perform an estimation of parameters to genus level using the known species.

Geometric Morphometric Analysis

Osteoderms were analysed using geometric morphometric methods (Bookstein, 1991; O’Higgins, 2000; Mitteroecker and Gunz, 2009). Eighteen two-dimensional landmark coordinates were digitalized from pictures of osteoderms using TPSDig (Rohlf, 2003). Not all osteoderms available in collections were used in this analysis due to missing, or not visible landmarks in some of them. Osteoderms that come from a specific region, such as pelvic shield, were considered anatomically homologous.

Four landmarks and 14 semi-landmarks dispositions on osteoderms are shown in Figure 1.1. Semi-landmarks were placed along the contour of the central figure and at the side edges, and the TPSUtil routine was used to allow semi-landmarks to slide so as to minimize bending energy (Rohlf, 2004). Landmark configurations were aligned, scaled, transposed and rotated using the generalized least squares Procrustes superimposition method (Bookstein, 1991; Dryden and Mardia, 1998; Rohlf and Slice, 1990; Slice et al., 1996). Centroid size (CS), a geometric scale defined as the square root of the sum of squared distances between all landmarks and the configurations centroid (Zelditch et al., 2004), was calculated for each osteoderm. Differences in CS between sample groups were assessed using one-way ANOVA. Generalized Procrustes analysis does not completely remove the effect of size and the relationship between size and shape remains. Here, presence of allometry (i.e., shape changes that are related to increases in size; Mosimann, 1970) was assessed through a multivariate regression of shape (Procrustes coordinates) against centroid size of osteoderms (Bookstein, 1991; Monteiro, 1999) using MorphoJ (Klingenberg, 2011). The amount of variation explained by allometry was quantified as the percentage of the total shape variation accounted for the regression model (Klingenberg and McIntyre, 1998), and the statistical significance of the model was assessed carrying out a permutation test (10,000 rounds). Significance of differences in shape between species was evaluated using a Procrustes Analysis of Variance (Procrustes ANOVA) in MorphoJ (analogous to a MANOVA) with 10,000 permutations. Then, canonical variates analysis (CVA) with 10,000 permutations were applied to the principal component scores to assess the discriminatory power of shape differences between groups. Shape differences along the first canonical variate axis were described using a wireframe graph.

Etymology. The species is named in honor of Hector Crispiani; biochemist, founder of the Museo de Ciencias Naturales ‘‘Florentino Ameghino’’ from Las Flores; an active promoter of the paleontology, who formed an abundant collection of fossils of the Pleistocene from Argentina during his life.

Stratigraphic and Geographic Provenance. Remains were found in "Pueblo Esther" in southeast of the Rosario city, Santa Fe province, (33° 05' 22" S and 60° 32' 38" W) in a level that is 7 m beneath the current ground surface, near the left margin of the Paraná River. MGPV-E1 comes from the Saladillo Formation (Parent et al., 2010), corresponding to late Pleistocene and Holocene. The bearing sediments consist of sandy silt with abundant carbonate. These are located below loessic sediments that may be correlated with Tezanos Pinto Formation (OIS2) (Kröhling and Orpheus, 2002).

Diagnosis. The pelvic shield osteoderms (Figure 2.1) are larger than those of E. seguini and E. pascuali and show until 8 surface foramina around the central figure. Surface foramina are larger than the 4-6 exposed on the surface of the fixed osteoderms of E. seguini (Figure 2.2, 2.3), and they are remarkably different in size of the fine punctuations of E. pascuali (Figure 2.4). Foramina around the central figure of pelvic shield osteoderms in many cases converge to form an oval opening (Figure 2.1). Five-six little hair follicle foramina on the posterior region of fixed osteoderms differs from the long 4 hair follicle foramina of E. seguini. Additional surface foramina between the anterior minor figures on most of the fixed osteoderms (Figure 2.1).

STATISTICS AND SHAPE ANALYSES

Statistical Analysis

Specimens of the previously recognized species of Eutatus were used to build a database to estimate parameters of the genus, such as width mean and length mean of fixed osteoderms, as well as estimate the variation within and between specimens (Table 1).

The analysis of width and length of the fixed osteoderms revealed that E. crispianii sp. nov. presented significantly wider (t-test, p < 0.0001) and longer osteoderms (t-test, p < 0.0001) than those belonging to previously described species (E. seguini + E. pascuali) (Krmpotic et al., 2009a). Figure 3 shows the correlation between width and length of the osteoderms of Eutatus. This reveals that many of the osteoderms of E. crispianii sp. nov. are outside the correlations ever observed between length and width in E. seguini or E. pascuali.

CVA showed that osteoderms of E. crispianii sp. nov. were located specifically in almost all cases in the positive values of the first axis. The most important shape variations along the CV1 were related to length of osteoderms and distance between the anterior border and the central figure (Figure 4). Positive values described osteoderms with shortening of the posterior region and extension of the region between the anterior border and the central figure. The negative values were related to more elongated and narrow osteoderms with less distance between the anterior border and the central figure. Moreover, osteoderms in the negative values of CV1 display greater distance between the central figure and the hair follicle foramina, placed in posterior region (Figure 4).

The major differentiation along CV2 was related to general changes in width and length of osteoderms. Positive values of CV2 were related to shorter and wider osteoderms while negative values were related to long and thin osteodems. E. crispianii sp. nov. adopted mostly positive values of CV2.

DISCUSSION

In cingulates the morphology of the osteoderms has been largely the basis of most of systematic schemes (Vizcaíno and Bargo, 1993; Vizcaíno et al.,1995; Soibelzon et al., 2010). However, the variations that exist within osteoderms from the dorsal carapace of a single individual, in Dasypodidae and Glytodontidae, has been subject of a large number of non-valid species generating the consequent overestimation of the diversity of these groups (Krmpotic et al, 2009a; Zurita et al., 2016, Cruz et al., 2016). To reduce the variation existing in the osteoderms due to location within the carapace, we have focused on a specific type of osteoderms from homologous regions between specimens. Moreover, it must be noted that in some cingulates, like Glyptodon spp., ontogenetic changes affect the morphology of the osteoderms, leading to a correlation between their size and their shape. This has also led to the creation of non-valid species based on juvenile or sub-adult specimens. This subject was recently reviewed by several authors (Zurita et al., 2011, 2016; Cruz et al., 2016) and the shape of osteoderms from a juvenile specimen of Glyptodon sp. were described (Luna and Krapovickas, 2011). However, detailed studies on phosteoderms of extant armadillos or Glyptodontidae using geometric morphometric techniques has not been tackled. In the present study we analysed the largest number of known osteoderms of Eutatus to cover the widest range of variations.

When we analysed the variation in shape versus the size of the osteoderms (Centroid Size), we observed that the main changes in shape are related very weakly to size. This shows that there are no severe changes in shape by varying the size of the osteoderms. In other words, variations in the size of the osteoderms does not modify to a large degree the shape of the osteoderms and the differences between E. seguini, E. pascuali and E. crispianii sp. nov. are due to intrinsic characteristics of each species.

Although some degree of overlap was observed in CVA (Figure 4), the differences in shape between the three species were statistically significant. These overlaps were expected due the intra-individual variation and the resultant high degree of variation in shape within each group.

E. crispianii has the biggest osteoderms, these surpass the width and length of those of E. pascuali and even of E. seguini, the other Lujanian specie (Figure 3). Osteoderms with widths greater than 17 mm were only observed in E. crispianii sp. nov. (Figure 3).

Statistical analysis showed that the width of the fixed osteoderms of the new species was significantly higher than the average of the previously described species (Table 1). Length variable also was on average higher than that observed for the heretofore known species of Eutatus (Table 1). In both cases, the probability that the osteoderms represented by the specimen MGPV-E1 come from a known species is negligible considering their width (p < 0.0001) and length (p < 0.0001). It is necessary to emphasize that the correlation between width and length of osteoderms of Eutatus showed that those of E. crispianii sp. nov were differentiable from E. seguini and E. pascuali, while the two latter were indistinguishable from each other (Figure 3).

From the morphological point of view, the presence of additional foramina near the anterior border (Figure 2.1, af), among the minor figures of fixed osteoderms, and away from the central figure, is a character that had not yet been observed in the genus Eutatus, although this feature is present in another member of the subfamily Euphractinae: Chaetophactus villosus (Krmpotic et al., 2009b; Francia and Ciancio, 2013).

The presence of abundant foramina was proposed as an adaptation to cold and dry climate in E. seguini (Krmpotic et al., 2009a). The greater abundance of exposed surface foramina, as well as its larger size in E. crispianii sp. nov. would be aligned with the arid or semi-arid climates occurred in lapses during the Lujanian Stage/Age in the northern Pampean region (Iriondo and García, 1993).

CONCLUSIONS

Landmark-based geometric morphometric analysis used in this study allowed evaluating morphological characteristics underlying the osteoderms of Eutatus species and include the complexity of the particular variation present in each osteoderm. This technique was suitable to include and assess the variation in shape that occurs not only between osteoderms of different specimens but also between neighboring osteoderms from a specific region within a same shield. Future research might explore the diversity of osteoderm of other Cingulata such as species of the family Glyptodontidae, which present great diversity in the osteoderms shape, even within the same specimen, in order to use this tool with systematics purposes.

Here we show that the larger size of the osteoderms, the large number and large size of the surface foramina, the short opening of the hair follicle foramina, and the novel presence of the additional foramina near the anterior border of the osteoderms are characters that are only combined in E. crispiannii.

Finally, the results presented here provide abundant evidence to consider E. seguini, E. pascuali and E. crispianii sp. nov. as separate taxonomic entities. The description of a new species of Eutatus increases the knowledge on the diversity achieved by the genus in the late Pleistocene. This also provides new clues about the organisms that inhabited the north of Pampean region, where faunistic association might have been somewhat different from those classic Lujanian faunas widely studied in the center and south of Pampean region (Tonni et al., 2003; Cione et al., 2009).

ACKNOWLEDGMENTS

We thank M. Reguero (MLP), A.A. Kramarz and S.M. Alvarez (MACN), C. Schreiber (MLFM), and H.G. Crispiani (MLF) for facilitating access to collections of their institutions. We thank M. Ciancio for critically reading and improving earlier drafts of the manuscript. We also express our gratitude to M.L. Irrazábal, F. García, G. Giordano, L. Rey and M.B. Molinengo for recovery and technical preparation of MGPV-E1. Thanks to H. Bottai and J.J. Ivancovich for their help in statistical analysis. J.L. Aguilar, J.I. Verdón of Paleontological Museum of San Pedro “Fray Manuel de Torres” and E. Aguirre of Museo de Antropología e Historia Natural “Los Desmochados” for their cooperation during the search for specimens. The comments of the editor J. Louys and three anonymous reviewer improved this work by providing constructive reviews.

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